1. Field of the Invention
The present invention relates generally to communication systems and, more particularly, to providing services, such as location-based services, in such communications systems.
2. Description of Related Art
As is well known, location-based services in a GPRS (General Packet Radio Service) network provide services to subscribers based on their current geographic location. The location-based services blend information about a person's location with other useful content, providing relevant, timely and local information to subscribers when and where it is needed. For example, location-based services can provide information about weather, traffic, restaurants, or retail stores, based on a subscriber's location at a particular moment in time.
GPRS is an extension to GSM (Global System for Mobile communication) technology. GPRS introduces packet switching to GSM networks. GPRS is a packet-based wireless communication technology that increases data rates of existing GSM networks and provides continuous connection to the internet for subscribers, such as mobile telephone and computer users. GPRS enables services such as color Internet browsing, e-mail “on the move,” powerful visual communications, and multimedia messages, in addition to the location-based services.
FIG. 1 shows a GPRS network architecture and a data transfer route in the GPRS network. The GPRS telecommunications network 100 includes a GGSN 112 (gateway GPRS support node) and a SGSN 110 (serving GPRS support node). The GGSN provides a gateway between the GPRS network and a public packet data network (PDN) or other GPRS networks. The GGSN provides interworking functionality with external packet data networks, acts as an access server, and sets up a logical link to a MS (mobile station) 102 through the SGSN. The MS is physical equipment, such as a mobile phone or laptop computer, used by mobile subscribers. When packet-switched data leaves the GPRS network, it is transferred to TCP-IP networks, such as X.25 or Internet 114. The SGSN controls the connection between the network and the MS. The SGSN provides session management and GPRS mobility management functions, such as handovers and paging. A PCU 108 converts packet data from the SGSN into a format that can be transferred to the MS and implements quality of service (QoS) measurements. A BSC 106, which is linked to the PCU, manages radio resources including a BTS (Base Transceiver Station) 104. The BTS is physical equipment, such as a radio tower, that is used to transmit radio frequencies over an air interface. The BSC may be connected to several BTS's. Each BTS may serve more than one MS. The BSC and BTS components, as a whole, are generally referred to as a BSS (Base Station System).
To initiate packet data transfer, first, the MS attaches itself to the GPRS network, and then activates a PDP (packet data protocol) context, thus activating a packet communication session between the MS, the SGSN and the GGSN. During the activation procedure, the MS either provides a static IP address or is provided with a temporary IP address from the GPRS network. The MS also specifies an APN (access point name). The APN provides routing information for SGSN and GGSN. The APN identifies the external service requested by a subscriber and specifies routing information. The MS requests a desired quality of service (QoS) and a NSAPI (network service access point identifier). The NSAPI is used to identify the data packets for a specific application since the MS can establish multiple PDP context sessions for different applications. Upon receiving information from the MS, the SGSN determines which GGSN is connected to the specified APN and forwards the request (i.e., IP data). Once the communication and activation procedure at the GGSN is successful, the IP data is transferred to external IP network 114 and to a server 116, and the appropriate response is forwarded to the MS from the server. During data transfer, the sending side (either the MS or the network) transmits blocks within a window, and the receiving side sends a packet uplink ack/nack (acknowledged/not acknowledged) or packet downlink ack/nack message, as needed.
The GPRS uses the existing GSM resources, such as spectrum, channels, and timeslots. The GPRS users share the same TDMA (Time Division Multiplexed Access) frame with the GSM voice users, thus increasing capacity requirements. Each TDMA frame is divided into eight consecutive slots of equal duration. To a certain extent, the GPRS takes care of increased capacity demand by multiplexing multiple users on the same physical channels (i.e., timeslots). Additionally, the GPRS dynamically allocate resources (i.e., timeslots) for voice and PDCHs (packet data channels).
FIG. 2 shows a GPRS data and signaling transmission plane. For example, assume that a subscriber in a taxi requests a location-based service using a GPRS mobile phone (i.e., MS 102), and a server provides the service. As shown in FIG. 1, the request is transferred to the BTS and the BSC, the PCU, the SGSN, and the GGSN. Thereafter, the request is forwarded to the Internet and then to the server. In response to the subscriber's request, the data is traveled from the Internet to GGSN 112, then to SGSN 110, to BSS 210 (i.e., BSC 106 and BTS 104), and finally to MS 104 (in this case, the subscriber's GPRS mobile phone). An application layer of the server generates an IP datagram and sends it across the external data communication network, such as IP or X.25, to GGSN 112. When the IP datagram arrives at the GGSN, it is called an N-PDU (network packet data unit) and it is addressed to a particular IP address. The GGSN maps each IP address to a GTP (GPRS Tunneling Protocol) identity. The data is passed down the GGSN protocol stack, as shown in FIG. 2, then transported over a physical layer of Gn interface to SGSN 110.
At SGSN 110, the N-PDU is relayed to a SNDCP (sub network dependent convergence protocol). The SNDCP compresses and segments the packet and sends the PDU to a LLC (logical link control) layer. The LLC layer provides a highly reliable logical connection between the SGSN and the MS. The LLC layer encapsulates the PDU in an LLC frame with its own header. The LLC header adds control information, frame check sequence, and SAPI (service access point identifiers) values. The data is then sent over a physical layer of Gb interface to the BSS 210, which encompasses BSC 106 and the BTS 104.
Next, a BSSGP (BSS GPRS protocol) layer at BSS 210 sends all of the information to a RLC (radio link control) layer. The RLC layer segments the LLC frames into smaller RLC blocks. A group of the LLC frames, which has been segmented into smaller blocks, is known as a TBF (temporary block flow). The TBF is assigned a TFI (temporary flow identity), and the RLC layer adds a header to the data blocks containing the TFI. A MAC (medium access control) layer controls the access signaling including assignment of uplink and downlink blocks. The MAC layer adds its own header, which is monitored by the MS. During the data transmission, the RLC/MAC messages will include the TFI in one of the fields to identify the receiving MS.
Thereafter, the data is transmitted over an air interface (i.e., Um) to the MS via a physical layer, GSM RF. Finally, the original information from the server is received at an application layer 250 by the mobile user (i.e., the subscriber).
As shown, the location-based services, like all other GPRS services, rely on accessing and utilizing centrally based services on a LAN or on the Internet, which results in a large quantity of data passing through the GSM/GPRS network. Further, to support the large quantity of data, the IP backbone/infrastructure has to be large. Otherwise it will result in poor performance across the network.
Accordingly, there is a need for providing GPRS services, such as the location-based services, without resulting in having such a large quantity of data communicated over the GSM/GPRS network.